1. Field of the Invention
The present invention relates to a method for preparing a (meth)acrylic acid ester. Particularly, the present invention relates to a method for preparing a (meth)acrylic acid ester by reacting (meth)acrylic acid with a C.sub.1-3 alcohol under specific conditions. Here, the term "(meth)acrylic" means each of "acrylic" and "methacrylic".
2. Discussion of Background
A (meth)acrylic acid ester is industrially important as a material for synthetic fibers, coating materials, adhesives, etc.
It is well known to use an ion exchange resin as a catalyst for the preparation of a (meth)acrylic acid ester by reacting (meth)acrylic acid with an alcohol. This reaction is an equilibrium reaction, and it is accordingly common to use one of the reactants, usually the alcohol, in excess in the reaction and to remove water formed by the reaction from the reaction system, to shift the equilibrium to increase the conversion.
As a method for removing water, various proposals have heretofore been made, such as a high temperature reaction, a reduced pressure reaction and a method by means of azeotropic distillation.
For example, JP-A-8-143512 proposes a method for preparing a (meth)acrylic acid ester by an esterification reaction of (meth)acrylic acid with a C.sub.1-8 alcohol in the presence of an ion exchange resin as a catalyst, wherein the reaction is carried out under reduced pressure, while the reaction liquid is circulated with heating to remove formed water whereby a high conversion is attained. However, this method has a drawback that the reaction liquid must be heated and circulated in order to attain the high conversion, and working Examples are limited to cases of higher alcohols having 4 or 6 carbon atoms.
JP-A-53-56611 proposes a method for preparing an acrylic acid ester by reacting acrylic acid with a higher alcohol in the presence of an ion exchange resin as a catalyst, wherein the reaction is carried out under reduced pressure using the alcohol in excess. In this case, it is disclosed that by carrying out the reaction under reduced pressure, a high conversion can be accomplished by one pass without using a solvent, the selectivity for the reaction is good as compared with reactions under atmospheric pressure, and the increase of by-products is slow. However, the reaction is carried out under a condition that the alcohol is in excess, whereby the proportion in formation of an alkoxypropionic acid and an alkoxypropionic acid ester is deviated to the alkoxypropionic acid ester. Accordingly, this method has a drawback that when the reaction is carried out by using a lower alcohol such as methanol, the alkoxypropionic acid ester will be distilled together with the acrylic acid ester in the purification system and tends to be accumulated in the purification system, whereby the load in the purification process tends to be large.
Further, JP-A-55-122740 proposes a method for preparing a (meth)acrylic acid ester by reacting (meth)acrylic acid with methanol or ethanol in the presence of an ion exchange resin as a catalyst, wherein the reaction is carried out by maintaining the reaction system in a gas-liquid mixed state while supplying the feed material to the reactor. In this case, for esterification of a lower alcohol, the reaction is not required to be carried out under reduced pressure, and it is disclosed that a high conversion can be accomplished by one pass by maintaining the gas-liquid mixed phase under atmospheric pressure. However, according to the study conducted by the present inventors, it was impossible to accomplish a conversion beyond a level equal to a liquid phase reaction even at a temperature at which a gas-liquid mixed phase is obtained under atmospheric pressure in the reaction of a lower alcohol. Further, this method has a drawback that the reaction temperature tends to be somewhat high in order to attain the gas-liquid mixed phase under atmospheric pressure, and thus it is likely to lead to a trouble that (meth)acrylic acid undergoes polymerization.
As described above, in a conventional esterification method which is carried-out in the presence of an excess amount of an alcohol, the conversion in the esterification reaction has not necessarily been adequate, and there has been a problem that the amount of resulting by-product such as an alkoxypropionic acid ester which will be problematic in the purification system or a polymer of an acrylic acid ester, is substantial.
Thus, it is an object of the present invention to provide a method whereby in the preparation of a (meth)acrylic acid ester by reacting (meth)acrylic acid with a C.sub.1-3 lower alcohol in the presence of an ion exchange resin as a catalyst, it is possible not only to improve the esterification yield by one pass but also to reduce as far as possible the amount of formation of a by-product which will be problematic in the purification system.